Rapid eye movement (REM) sleep behavior disorder (RBD) involves REM sleep without atonia in conjunction with a recurrent nocturnal dream enactment behavior, with vocalizations such as shouting and screaming, and motor behaviors such as punching and kicking. Secondary RBD is well described in association with neurological disorders including Parkinson's disease (PD), multiple system atrophy (MSA), and other conditions involving brainstem structures such as tumors. However, RBD alone is now considered to be a potential harbinger of later development of neurodegenerative disorders, in particular PD, MSA, dementia with Lewy bodies (DLB), and pure autonomic failure. These conditions are linked by their underpinning pathology of alpha-synuclein protein aggregation. In RBD, it is therefore important to recognize the potential risk for later development of an alpha-synucleinopathy, and to investigate for other potential causes such as medications. Other signs and symptoms have been described in RBD, such as orthostatic hypotension, or depression. While it is important to recognize these features to improve patient management, they may ultimately provide clinical clues that will lead to risk stratification for phenoconversion. A critical need is to improve our ability to counsel patients, particularly with regard to prognosis. The ability to identify who, of those with RBD, is at high risk for later neurodegenerative disorders will be paramount, and would in addition advance our understanding of the prodromal stages of the alpha-synucleinopathies. Moreover, recognition of at-risk individuals for neurodegenerative disorders may ultimately provide a platform for the testing of possible neuroprotective agents for these neurodegenerative disorders.

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Obstructive sleep apnea (OSA) has been found to be an independent risk factor for stroke in large epidemiological studies. The mechanisms underlying this relationship have been investigated over the past 2-3 decades, with a particular focus on identifying pathophysiological pathways and risk modification strategies. Despite the advancements made, the specific understanding of the implicated mechanisms is still limited. This brief review focuses on presenting some of the epidemiological evidence of the linkage between OSA and stroke, discussing mechanistic pathways and the potential effect of OSA treatment in modulating the risk for stroke in these patients. Future directions for research in this field are also discussed.

Dream enactment behavior is a phenomenon demonstrated in patients with post-traumatic stress disorder, rapid eye movement sleep behavior disorder, as well as with a more recently described condition entitled trauma-associated sleep disorder, which shares diagnostic criteria for rapid eye movement sleep behavior disorder. While these conditions share some commonalities, namely dream enactment behavior, they are quite different in pathophysiology and underlying mechanisms. This review will focus on these 3 conditions, with the purpose of increasing awareness for trauma-associated sleep disorder in particular.

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